The invention relates to a method for thin needle biopsy or tissue marking of a patient's mammary gland in connection with mammography, and an assembly which enables a suspect site in the tissue to be localized and a thin needle biopsy specimen to be taken of it. In the method, a stationary target is radiographed from two angles by means of a rotating picture head, the pictures are placed on a separate measurement table, and the x, y and z coordinates of the desired site in the target are calculated in a known manner on the basis of the two pictures.
Especially in connection with mammographic examinations it is often necessary to localize some interesting site in the target, for example for biopsy. In connection with mammography, usually thin needle biopsy is used, for example for the diagnosis of cancer. Furthermore, in connection with thin needle biopsy it is possible to mark the interesting site with a thin thread in order to facilitate a surgical operation following the biopsy. The method used for localizing the target is known per se. WP publication 88/01847 describes a method and apparatus for stereotactic biopsy of pathological sites in the breast. In the method, the target is radiographed from two directions, and the location of the pathological site is determined on the basis of these two pictures. In this method the picture head and the film are maintained stationary, and the target is moved in the horizontal direction in order to obtain a pair of pictures. The method is inconvenient for the patient, and the accuracy of the method may suffer as the patient has to move between the taking of the pictures.
EP Patent Application 0146511 also presents a method for the localization of a three-dimensional target point within the target by using X-rays. In this method the target is radiographed from two directions, and on the basis of these pictures the location coordinates x, y and z of the target point are calculated automatically by computer. These coordinates are mediated to motors which move the needle guide and thereby the needle. When the needle has been aligned, the motor which moves the needle vertically starts, and the specimen is taken automatically. However, this known method has the disadvantages of being expensive owing to its automation and motorization, and of being non-patient-friendly, since the patient has to be at the "mercy" of the machine and has to trust in automation, and this may, especially in older people, arouse repugnance against the examination.